1. Field of the Invention
The present invention relates to a semiconductor device that comprises a plurality of drivers that drive, for example, a liquid crystal display unit of a liquid crystal display device as a load by means of a drive signal, and to a driver, for example.
2. Description of the Related Art
Normally, in a liquid crystal display device that comprises a matrix color liquid crystal panel, for example, as a liquid crystal display unit, a scanning line driver, which drives the liquid crystal panel scanning lines, and a signal line driver, which drives the signal lines, are provided as the liquid crystal panel drivers that drive the liquid crystal panel.
These liquid crystal panel drivers are mounted by means of the COG method on the same substrate as the liquid crystal panel to form a semiconductor-device integrated circuit. For example, in the case of the semiconductor device that constitutes the scanning line driver, for a single liquid crystal panel, a plurality of liquid crystal display drivers, which drive the respective liquid crystal display blocks formed as blocks in a plurality of rows of the scanning lines, is arranged and cascade-connected so that the respective supply wires of these liquid crystal display devices are sequentially connected.
The conventional semiconductor device above will be described hereinbelow with reference to the drawings.
FIG. 1 is an equivalent circuit diagram showing the constitution of a liquid crystal display device that uses a conventional semiconductor device. As the conventional semiconductor device, a case where a plurality of liquid crystal display drivers mounted by means of the COG method is constituted by means of a cascade connection is shown.
In the case of the semiconductor device shown in FIG. 1, arranged in the liquid crystal display device 1, whose liquid crystal display unit 2 is the load, is a plurality of liquid crystal display drivers (1) 3-1 to (N) 3-n, which are each connected to drive each liquid crystal display block of liquid crystal display blocks (1) 2-1 to (N) 2-n that are operationally separated to form a plurality. Each liquid crystal display driver 3 is formed having an output terminal 4 that outputs a drive signal for driving the liquid crystal display blocks of the liquid crystal display unit 2 (although not illustrated, this output terminal comprises a drive unit that generates a drive signal), and a drive supply line 5, which is supply wiring, for supplying a power supply (A, B) 6 allowing the drive unit to generate a drive signal. These liquid crystal display drivers 3 are cascade-connected such that the drive supply lines 5 are sequentially connected via wire wound resistors R, and, as a result of the mutual cascade connection between the liquid crystal display drivers, the power supply (A, B) 6 is supplied to the subsequent-stage liquid crystal display drivers via the wirewound resistors R between the liquid crystal display drivers.
Further, the internal constitution of the conventional liquid crystal display driver is shown in FIG. 5. A clock signal 7, an operation start signal 8, a power supply (A) 6A, a power supply (B) 6B, and another plurality of input signals 9 are input to the liquid crystal display driver 3. The input signals 9 and supplies (A, B) 6 are also transmitted as signals by means of the cascade connection. In the case of this liquid crystal display driver 3, when the clock signal 7 and operation start signal 8 are input to a shift register 10, the operation start signal 8 is sequentially transferred to the shift register 10 in accordance with the timing of the clock signal 7.
The output of the shift register 10 is input to a level shifter 11 and converted to an amplitude signal that is determined by the respective potentials of the power supply (A) 6A and power supply (B) 6B. When the row electrodes in the scanning line direction of the liquid crystal display unit 2 are driven, the potential of the power supply (A) 6A is individually output in sequence by the respective output terminals 4 arranged in the liquid crystal display driver 3. Then, the potential of the power supply (B) 6B is output to the liquid crystal display unit connected outside the driven rows. Subsequently, when the drive voltage output from all the output terminals 4 sequentially arranged is complete, an operation end signal 12 is output. The operation end signal 12 is the operation start signal of the subsequent-stage liquid crystal display driver when a cascade connection is in place.
In the case of this conventional liquid crystal display driver 3, when the liquid crystal display unit is driven, a precharge/discharge current of a liquid crystal capacitance Y1 generated by the liquid crystal element shown in FIG. 1 flows sequentially to the power supply (B) 6B via each output terminal 4.
Further, in the case of conventional semiconductor devices, which drive the liquid crystal display blocks of the liquid crystal display unit 2 by means of the respective liquid crystal display drivers 3 by cascade-connecting a plurality of the liquid crystal display drivers 3, as shown in FIG. 3A, each drive supply line 5 is sequentially connected via wirewound resistors R between the liquid crystal display drivers 3. Hence, when a precharge/discharge current I of the liquid crystal capacitance Y1 generated by each liquid crystal element forming the liquid crystal display unit 2 flows, an output-voltage potential difference ΔV(=I·R) is generated across A and B, and C and D of the liquid crystal display drivers 3, as shown in FIG. 3B.
Because this potential difference ΔV is generated, the potential of the power supply (B) 6B, which is the power supply when no driving is taking place, is nonuniform in the liquid crystal display drivers 3, and hence a display variation, which arises from a display variation of the undriven liquid crystal display unit between the liquid crystal display blocks of the liquid crystal display unit 2 (a phenomenon according to which, although the liquid crystal display is dark when no drive is taking place, this darkness is subject to a variation), is generated, there is the problem that a striped pattern is produced on the display screen.